Temporal dynamics of the Chlorophyll a-Total phosphorus relationship and algal production efficiency: Drivers and management implications

In recent decades, climate change has significantly affected water quality and algal blooms in lakes worldwide. Studying the temporal dynamics patterns of algal production efficiency and its drivers in individual lakes is useful for analyzing the evolutionary trajectory of Chla-TP changes, and identifying the main controlling factors of eutrophication to guide lake management. In this study, we used a dataset for the Lake Gehu (1986-2020) to analyze the drivers of the ETP variability on interannual and seasonal time scales and to quantify the relative impacts and contributions of nutrient and climatic factors on the ETP. The results showed a negative correlation of the Chla-TP relationship appeared in years with very high ETP. The effects of nutritional and climatic factors on the ETP at different time scales were quantified using a generalized additive model. The results showed that the total phosphorus (TP) concentration had a significant effect on the interannual ETP variation, explaining up to 28.9 %. At the intra-annual scale, climatic variables had a much greater effect on the ETP than the nutrient concentration, and the explanatory effect was ranked as temperature > wind speed > rainfall > total nitrogen (TN). Based on the characteristics of seasonal ETP variations, the TPa of Lake Gehu were 50 mu g/L, 33 mu g/L, 20 mu g/L with ETP levels of 0.2, 0.3, 0.5, respectively. This research highlights the significance of nutrient and cli-matic factors in interannual and seasonal scale, respectively. In addition, ETP influenced by the coupling of nutrient and climate provides a criterion for establishing the seasonal nutrient threshold of lakes.